→Mathematics
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{{ | {{guidenote}} | ||
''' | '''Armour Class''' ('''AC''') is a measurement of how difficult a creature is to be hit by an attack. In order to successfully hit a creature, the results of an [[Attack roll|attack roll]] must have a number equal to or greater than the target's Armour Class. AC can be increased by equipping [[Armour|armour]] and [[Shields|shields]], by selecting certain [[Feats|feats]] when leveling up, or utilizing certain [[Spells|spells]]. | ||
The formula that determines AC is: | == Formulas == | ||
The default formula that determines AC is: | |||
: {{InfoBlob|10 + [[Dexterity|Dexterity modifier]] + armour bonus + shield bonus + other bonuses and penalties}} | |||
The AC bonus from Dexterity modifier may be capped when wearing [[Armour#Medium armour|medium]] and is ignored entirely when wearing [[Armour#Heavy armour|heavy]] armour. | |||
Medium armour caps the Dexterity Modifier to +2,{{note|The [[Medium Armour Master]] feat increases the cap from +2 to +3.}}{{note|Four rare armours have an "Exotic Material" trait that allow the wearer to get the full Dexterity bonus to AC, namely [[Yuan-Ti Scale Mail]], [[Unwanted Masterwork Scalemail]], [[Sharpened Snare Cuirass]], and [[Armour of Agility]].}} whereas heavy armour ignores the modifier entirely. | |||
Shields will grant the listed AC bonus to whomever equips it, regardless of which weapon slot they are currently using. | |||
=== Other formulas === | |||
Unarmoured creatures may use one of the following different formulas if they have certain features. Creatures always use whichever formula – which they have access to – would result in a higher AC.{{note|Alternative formulas are only used if {{em|no}} items are worn in the chest, hands, helm or boots slots which are labelled as armour.|name=slots}} | |||
{{SAI|Mage Armour}} or {{SAI|Draconic Resilience}}: | |||
: {{InfoBlob|13 + Dexterity modifier + shield bonus + other bonuses and penalties}} | |||
{{SAI|Unarmoured Defence (Barbarian)}}: | |||
: {{InfoBlob|10 + Constitution modifier + Dexterity modifier + shield bonus + other bonuses and penalties}} | |||
{{SAI|Unarmoured Defence (Monk)}}: | |||
: {{InfoBlob|10 + Wisdom modifier + Dexterity modifier + other bonuses and penalties}} | |||
== Mathematics== | |||
Armour Class becomes more useful the greater it is – the difference in effectiveness between 20 and 19 AC is {{em|greater}} than the difference in effectiveness between 16 and 15. | |||
To illustrate this, if a defender has 15 AC and 10 HP, and the attacker has +5 (50% chance to hit) to attack rolls, and deals 2 damage per attack, the defender would on average survive for 10 turns. | |||
If the defender's AC was increased to 16 (45% chance to be hit), they would instead survive for an average of 11.1 rounds (an 11% increase in effectiveness). | |||
Meanwhile, if the defender has 19 AC (30% chance to be hit), they would survive for an average of 16.66 rounds. If their AC was increased to 20 (25% chance to be hit), they would be able to survive for an average of 20 rounds (a 20% increase in effectiveness). | |||
The difference between 25 and 24 is even greater, with a {{em|100%}} increase in effectiveness (50 vs 100 rounds). | |||
== Footnotes == | |||
{{notelist}} | |||
{{NavGameplay}} | |||
[[Category:Gameplay mechanics]] |